Avian Lymphoid Leukosis (LL)

Avian lymphoid leukosis is a neoplastic disease of chickens caused by a virus of the leukosis/sarcoma group and characterized by tumor formation of the bursa of Fabricius with metastasis to other tissues and all abdominal organs.

Avian lymphoid leukosis Signs:

Depression

Emaciation

Loss of weight

Persistent low mortality

Enlargement of abdomen, liver or bursa

Many are asymptomatic.

There are several manifestations: Lymphoid leukosis, myeloid leucosis (myeloblastosis, granuloblastosis), erythroid leukosis (erythroblastosis) hemangioendothelioma (tumors comprised of blood vessels), and osteopetrosis (bone leukosis). Susceptibility starts in ovo but decreases with age of the bird.

Birds are most susceptible when young, but LL is seldom seen in broilers due to the long incubation period. The female is more susceptible than the male to all forms of LL except osteopetrosis, to which the cockerel is more susceptible. Stresses from other diseases increase the severity of leukosis. Because the virus has a long incubation period, signs are not noticeable until birds are 16 weeks or older.

Diagnosis based on flock history and tumors, confirmed by typical progression of disease and differentiation from other diseases. There is no treatment. Prevention is to obtain chicks from LL-free sources, rear birds in isolation with adequate ventilation and biosecurity, prevent stress and control other diseases.